1. Field of Invention
The present invention generally relates to fibers, methods of making fibers and to products made thereof. More particularly, the present invention relates to polypropylene fibers that can comprise isotactic polypropylene and syndiotactic polypropylene. In another aspect, the invention relates to bicomponent fibers comprising isotactic polypropylene and syndiotactic polypropylene, to methods of making such bicomponent fibers of isotactic polypropylene and syndiotactic polypropylene, and to products made from such bicomponent fibers of isotactic polypropylene and syndiotactic polypropylene.
2. Description of the Related Art
Polypropylene has found employment in a wide variety of applications. Examples of uses include nonwoven fabrics such as spun bonded, melt blown, thermally bonded and carded staple fibers uses for applications such as diaper components and medical fabrics where properties such as bulk and softness are important. Polypropylene fibers have found commercial use in synthetic carpets, geotextiles, textile fabrics and the like. While polypropylene fibers have found wide application as carpet yarns, polypropylene fibers can lack the elasticity and resiliency of other carpet fiber polymers, for example, nylon. When loads such as furniture legs rest on polypropylene carpets for an extended period are removed, they can leave their impression on the carpet in the form of packed carpet fibers. Poor resiliency prevents the packed fibers from returning back to their original configuration, which can be referred to as elastic recovery.
Bicomponent fibers can comprise a first polymer component and a second component, with each component fused to the other along the fiber axis. The first and second components may be configured as core and sheath, side by side, tipped, mocro denier and mixed fibers, and are generally produced utilizing a specially equipped fiber spinning machine. Examples of bicomponent fibers include nylon and polyurethane, and polypropylene and polyethylene copolymers.
Bicomponent fibers of isotactic polypropylene and syndiotactic polypropylene have been disclosed in U.S. Pat. No. 6,074,590, issued Jun. 13, 2000, and in U.S. Pat. No. 6,395,392, issued May 28, 2002, both to Gownder, herein incorporated by reference. Isotactic propylene (iPP) may generally be described as having methyl groups attached to the tertiary carbon atoms of successive monomeric units on the same side of a hypothetical plane through the polymer chain. Syndiotactic polypropylene (sPP) may generally be described as having methyl groups attached on alternating sides of the polymer chain. While various combinations of syndiotactic and isotactic polypropylene have been proposed, there is still a need in the art for improved bicomponent fibers.